[Wasm GC] Support and fuzz function subtyping (#5420)

Support function subtyping with contravariant parameters and covariant results.
The actual change is a single line in wasm-type.cpp, so most of the patch is
updating the type fuzzer to generate interesting function subtypes. Since
function parameters are covariant, generating a function subtype requires
generating supertypes of its parameter types, which required new functionality
in the fuzzer. Also update the fuzzer to choose to reuse types at a finer grain,
so for example individual function parameters or results might be reused
unmodified while other parameters or results are still modified.

0 files changed, 0 insertions, 0 deletions